Parallelism refers to giving each element in a list the same grammatical category (noun phrases, verb clauses, infinitives, etc.). The similarity of the grammatical form makes it easier for readers to perceive a similarity in content and function. The sentence below is not parallel.
 | The students’ objections were the injustice of the measures and that they were unconstitutional. |
The first element of the list (
the injustice of the measures) is a noun phrase while the second (
they were unconstitutional) is a verb clause. The sentence would be more readily understandable if it were rewritten. The sentence below contains a verb instead of the nominalization
objections and then has a verb clause that contains a list of two elements, both of which are adjectives.
 | The students objected that the measures were unjust and unconstitutional. |
In any series of items, then, make sure that each element of the series is in exactly the same form as all of the others. In other words, don't follow the example below, where the writer tries to combine two noun phrases (
the personality and
the contacts) with a verb clause (
have the knowledge).
| The students taking this master’s degree will acquire the personality, the contacts and have the knowledge to succeed in almost any business venture. |
Instead, rephrase the sentence like this:
| The students taking this master’s degree will acquire the personality, the contacts and the knowledge to succeed in almost any business venture. |
This general guideline can affect even the smallest, and seemingly trivial, of words. Therefore, not
| The Erasmus students will talk of their experiences in Paris, in Athens and Moscow. |
but
| The Erasmus students will talk of their experiences in Paris, Athens and Moscow. |
The principle of parallelism should also be respected in vertical lists. Therefore, not
| Students must
a) present the official application form,
b) their personal academic certificate, and
c) proof of payment. |
but
| Students must present
a) the official application form,
b) their personal academic certificate, and
c) proof of payment. |
Take particular care when you use such structures as
not only ... but also. Therefore, not
| Master’s degrees not only prepare professionals but also researchers. |
but
| Master’s degrees prepare not only professionals but also researchers. |
